5.6.1 A Simple Style File

The example is from the AUCTeX sources and is loaded for any LaTeX
document using the book document class (or style before LaTeX2e).
The file specifies that the largest kind of section in such a document
is chapter. The interesting thing to notice is that the style file
defines an (anonymous) function, and adds it to the list of loaded style
hooks by calling TeX-add-style-hook.

The first time the user indirectly tries to access some style-specific
information, such as the largest sectioning command available, the style
hooks for all files directly or indirectly read by the current document
are executed. The actual files will only be evaluated once, but the
hooks will be called for each buffer using the style file.

Note that the basename of the style file and the name of the style hook
should usually be identical.

Function:TeX-add-style-hookstylehook &optional dialect-expr

Add hook to the list of functions to run when we use the TeX
file style and the current dialect is one in the set derived from
dialect-expr. When dialect-expr is omitted, then hook
is allowed to be run whatever the current dialect is.

dialect-expr may be one of:

A symbol indicating a singleton containing one basic TeX dialect,
this symbol shall be selected among:

:latex

For all files in LaTeX mode, or any mode derived thereof

:bibtex

For all files in BibTeX mode, or any mode derived thereof

:texinfo

For all files in Texinfo mode.

A logical expression like:

(or dialect-expression1 … dialect-expression_n)

For union of the sets of dialects corresponding to dialect-expression1
through dialect-expression_n

(and dialect-expression1 … dialect-expression_n)

For intersection of the sets of dialects corresponding to
dialect-expression1 through dialect-expression_n

(nor dialect-expression1 … dialect-expression_n)

For complement of the union sets of dialects corresponding to
dialect-expression1 through dialect-expression_n
relatively to the set of all supported dialects

(not dialect-expr)

For complement set of dialect corresponding to dialect-expr
relatively to the set of all supported dialects

In case of adding a style hook for LaTeX, when calling function
TeX-add-style-hook it is thought more futureproof for argument
dialect-expr to pass constant LaTeX-dialect currently
defined to :latex, rather than passing :latex directly.

Constant:LaTeX-dialect

Default dialect for use with function TeX-add-style-hook for
argument dialect-expr when the hook is to be run only on LaTeX
file, or any mode derived thereof.